U0275 — Lost Communication Lighting Driver Control Module C

Generic OBD-II · all makesNetwork / communication

U0275 indicates that the Powertrain Control Module (PCM) has lost communication with the Lighting Driver Control Module (LDCM) on the C side of the vehicle network. The PCM detects a timeout or abnormal response from the LDCM and stores this diagnostic trouble code.

Symptoms

Exterior lights (headlamps, fog lamps, turn signals) may flicker, dim, or fail to operate correctly
Dashboard illumination may be inconsistent or go out completely
Warning lamp (e.g., “Service Lamp” or “Lighting System” indicator) illuminates on the instrument cluster
Accessory power (e.g., interior lights, power sockets) may be intermittent
Vehicle may exhibit reduced visibility at night due to dimmed lighting

What causes it — most likely first

1. Faulty Lighting Driver Control Module (C side)

Internal failure of the LDCM such as blown driver transistors or corrupted firmware prevents it from responding to PCM requests.

2. Wiring harness damage or connector corrosion

Broken, frayed, or corroded wires, or loose pins in the connector between the PCM and LDCM, can interrupt communication.

3. Ground or power supply problem to the LDCM

Insufficient voltage or a bad ground reference can cause the LDCM to stop transmitting data.

4. Faulty PCM communication circuit

A defect in the PCM’s CAN transceiver or communication line may prevent it from receiving the LDCM’s response, though this is less common.

How it's diagnosed

Verify that the “Lighting System” or related warning lamp is illuminated and note any abnormal lighting behavior.
Inspect the wiring harness and connectors between the PCM and the LDCM for damage, corrosion, or looseness; repair or reseat as needed.
Check voltage and ground at the LDCM power pins with a multimeter while the lights are commanded on; ensure they meet specifications.
Use a scan tool to perform a bidirectional test or live data read of the LDCM; observe whether the module acknowledges PCM commands.
If the LDCM does not respond after wiring and power checks, replace the LDCM and clear the code; re‑test to confirm resolution.

Code facts & related codes

SystemNetwork / communication

StandardizationSAE generic — identical on every make

Frequently asked

Can the PCM be replaced to fix a U0275 code?

Replacing the PCM is rarely the correct solution. In most cases the problem lies with the LDCM, its wiring, or its power/ground. PCM replacement should only be considered after all other possibilities have been eliminated and a PCM fault has been confirmed.

Will resetting the code clear the problem?

Clearing the code without addressing the underlying issue will only cause the code to return, often immediately, because communication loss still exists.

Is a blown fuse a possible cause?

Yes. A fuse that supplies power to the LDCM can cause loss of communication. Check the relevant fuse(s) in the fuse box and replace any that are open.

Can a bad battery or alternator cause U0275?

A severely low battery voltage or alternator output can affect the LDCM’s power supply, leading to communication loss. Verify that the vehicle’s charging system is operating within normal voltage ranges before concluding the fault is in the lighting module.